Graphene sheets are a novel carbon material exhibiting quantized conduction (ballistic conduction) in the same manner as carbon nanotubes, and are attracting attention as a next-generation technology for fabricating low-resistance interconnects to replace metal interconnects. Because the mean free path of electrons in a graphene sheet is very long, that is, about 100 nm to 1 μm, graphene sheets are highly advantageous in electrical conduction in a long interconnect. A graphene sheet is formed on an exposed face of a catalyst layer by CVD or the like. Because an edge portion of a graphene sheet has the lowest electrical resistance in the graphene sheet, a method for forming a plurality of edges in a graphene sheet is required.